Malignant mesothelioma is an asbestos-associated neoplasm which is a growing public health concern and which poses tremendous diagnostic and therapeutic challenges. At least 65% of mesotheliomas have deletion of the mid- portion of the chromosome 6 long arm, and it is notable that this same region is deleted nonrandomly in breast cancer, leukemia, non-Hodgkin's lymphoma, osteosarcoma, and prostate cancer. Dr. Fletcher and coworkers hypothesize that a tumor suppressor gene in the 6q16.3-q21 region is deleted and/or mutated in the majority of mesotheliomas, and they also hypothesize that this gene has broad relevance in non-mesothelioma tumorigenesis. Dr. Fletcher will address these hypotheses by fine mapping of the 6q deletion region, by mapping, isolating, and characterizing balanced cytogenetic rearrangements that interrupt this region, and by evaluating candidate tumor suppressor genes in mesotheliomas and in non- mesothelioma tumors with 6q deletions. Mapping will be performed in two phases. Initially, Dr. Fletcher will map a broad region of the chromosome 6 long arm in 30 primary mesotheliomas in cell lines using an established 10-member FISH panel of mega-YACs spaced at 2-10 megabase intervals. This phase of mapping will define the critical deletion region while simultaneously evaluating the possibility of additional deletion regions. In the second phase Dr. Fletcher will re-evaluate the same group of mesotheliomas using a bacterial artificial chromosome (BAC) FISH panel spanning the critical deletion region at 500 kb intervals. These studies may reveal cytogenetically in apparent heterozygous and homozygous deletions which will further narrow the critical deletion region. The deletion mapping will be coordinated with mega-YAC FISH mapping and cloning of breakpoints for balanced cytogenetic rearrangements within the consensus deletion region. Screening for candidate tumor suppressor genes will then be accomplished by direct cDNA selection using 100-250 kb BAC DNA sequences containing the critical deletion region and a cytogenetic breakpoint. Candidate tumor suppressor genes will be evaluated with a respect to copy number (FISH), inactivating point mutations (SSCP/sequencing), and expression (Northern blotting) in primary mesotheliomas, mesothelioma cell lines, and in non- mesothelioma cancers with known 6q deletions. Long-term objectives include evaluation of the 6q tumor suppressor gene as a potential diagnostic marker in mesothelioma and evaluation of the biological elements of this gene through functional studies.